Methods for improving corrosion resistance and applications in electrical connectors

ABSTRACT

A method of manufacturing an electrical conductor includes providing a substrate layer, depositing a graphene layer on the substrate layer and selectively depositing boundary cappings on defects of the graphene layer to inhibit corrosion of the substrate layer at the defects. Optionally, the boundary cappings may include nano-sized crystals deposited only at the defects. The selectively depositing may include electrodepositing boundary cappings on exposed portions of the substrate layer at the defects. The selectively depositing may include reacting boundary capping material with exposed portions of the substrate layer at the defects to deposit the boundary cappings only at the defects.

BACKGROUND OF THE INVENTION

The subject matter herein relates generally to methods for improvingcorrosion resistance and applications in electrical connectors.

Electrical conductors have many forms, such as a contact, a terminal, apin, a socket, an eye-of-needle pin, a micro-action pin, a compliantpin, a wire, a cable braid, a trace, a pad and the like. Such electricalconductors are used in many different types of products or devices,including electrical connectors, cables, printed circuit boards, and thelike. The metals used in the electrical conductors are susceptible tocorrosion, diffusion or other reactions, limiting their use or requiringprotective coatings. For example, when copper or copper alloy electricalconductors are used, such conductors are susceptible to corrosion.Corrosion of base metals is detrimental to the conductor interface andsignal integrity. A gold surface layer is typically applied to thecopper as a corrosion inhibitor. However, the gold surface layer addsexpense to the electrical conductor.

Grapheme has shown to be promising in electronics devices as a corrosionresistance layer due to the conductivity and chemically stable nature ofgraphene. However, grain boundaries and other defects of the graphenelayer are weak points vulnerable to corrosion attacks. The cost tomanufacture large graphene grains, having less boundary area and fewerdefects, are extremely high and time consuming to manufacture.

A need remains for an electrical conductor that addresses theaforementioned problems and other shortcomings associated withtraditional electrical conductors.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method of manufacturing an electrical conductorincludes providing a substrate layer, depositing a graphene layer on thesubstrate layer and selectively depositing boundary cappings on defectsof the graphene layer to inhibit corrosion of the substrate layer at thedefects.

Optionally, the boundary cappings may include nano-sized crystalsdeposited only at the defects. The selectively depositing may includeelectrodepositing boundary cappings on exposed portions of the substratelayer at the defects. The selectively depositing may include reactingboundary capping material with exposed portions of the substrate layerat the defects to deposit the boundary cappings only at the defects. Theselectively depositing may include selectively depositing boundarycappings of nano-sized crystals of precious metal using a process thatreacts the nano-sized crystals of precious metals with the substratelayer exposed at the defects and that does not react the nano-sizedcrystal of precious metal with the graphene layer.

Optionally, the selectively depositing may include an atomic layerdeposition process in select locations at the defects or aself-assembled monomer process in select locations at the defects. Theselectively depositing may include providing a precursor that reactswith the substrate layer and the boundary capping material and that doesnot react with the graphene layer to selectively deposit the boundarycapping material at the locations of the defects where the substratelayer is exposed. The selectively depositing may include filling thedefects with boundary capping material such that the boundary cappingmaterial is deposited directly on the substrate layer in the graphenelayer.

Optionally, the depositing a graphene layer on the substrate layer mayinclude depositing of graphene layer with defect-free areas betweendefects of the graphene layer. The selectively depositing may includeselectively depositing boundary cappings on the defects with thedefect-free areas largely devoid of boundary cappings.

In another embodiment, a method of manufacturing an electrical conductorincludes providing a substrate layer, depositing a graphene layer on thesubstrate layer having defects exposing the substrate layer, anddecorating the defects with metal boundary cappings. The defects aredecorated with the metal boundary cappings using an electrodepositionprocess where nano-size crystals of the metal boundary cappings aredeposited at the exposed portions of the substrate layer.

In a further embodiment, an electrical conductor is provided having asubstrate layer, a graphene layer deposited on the substrate layerhaving defects exposing the substrate layer, and boundary cappings atthe defects. The boundary cappings inhibit corrosion of the substratelayer at the defects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a portion of an electrical conductorformed in accordance with an exemplary embodiment.

FIG. 2 is a top view of a portion of the electrical conductor 100showing a graphene layer and boundary cappings to inhibit corrosion ofthe electrical conductor.

FIG. 3 is an enlarged view of a portion of the electrical conductorshown in FIG. 2.

FIG. 4 is a flow chart of an exemplary method of manufacture of anelectrical conductor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross sectional view of a portion of an electrical conductor100 formed in accordance with an exemplary embodiment. The electricalconductor 100 may be any type of electrical conductor, such as acontact, a terminal, a pin, a socket, an eye-of-the-needle pin, amicro-action pin, a compliant pin, a wire, a cable braid, a trace, a padand the like. The electrical conductor 100 may form part of anelectrical connector, a cable, a printed circuit board and the like.

In an exemplary embodiment, the electrical conductor 100 is amulti-layered structure having a substrate layer 102 and a surface layer104. The substrate layer 102 is a metal substrate (e.g. copper, copperalloy, nickel or nickel alloy). The substrate layer 102 may be amulti-layered structure. In an exemplary embodiment, the substrate layer102 is electrically conductive and includes a metal compound, such as acopper or a copper alloy. Other metal compounds for the substrate layer102 may include nickel, nickel alloy, steel, steel alloy, aluminum,aluminum alloy, palladium-nickel, tin, tin alloy, cobalt, tungsten,platinum, palladium, carbon, graphite, graphene, carbon-based fabric, orany other conductive material. Optionally, the substrate layer 102 mayinclude one or more barrier layers that provide a diffusion barrierbetween the metal of the metal substrate and the surface layer 104.

In an exemplary embodiment, the surface layer 104 provides acorrosion-resistant electrically conductive layer on the substrate layer102. The surface layer 104 protects the substrate layer 102, such asfrom corrosion, and/or enhances the characteristics of the substratelayer 102, such as by reducing friction enhancing wear resistance, andthe like. In an exemplary embodiment, the surface layer 104 includes agraphene layer 106 deposited on the substrate layer 102 and boundarycappings 108 selectively deposited on the graphene layer 106 and/or thesubstrate layer 102. The graphene layer 106 is provided on the substratelayer 102 to inhibit corrosion of the substrate layer 102. The boundarycappings 108 are provided to fill, either partially or entirely, defects110 in the graphene layer 106 to inhibit corrosion in the area of thedefects 110. Other types of carbon-based structures, such as a layer ofcarbon nanotubes (CNTs), a graphite oxide structure, and the like may beused rather than graphene in the surface layer 104. The carbon-basedstructures are electrically conductive and provide corrosion resistanceas well as other features. In an exemplary embodiment, the carbon-basedstructure is used on a copper base in-lieu of traditional nickel andgold platings on the copper base.

The surface layer 104 is generally a thin layer, as compared to thesubstrate layer 102. The surface layer 104 may be deposited on thesubstrate layer 102 by any known process, such as deposition, plating,adhering, and the like. Optionally, the surface layer 104 may bedeposited directly on the underlying substrate layer 102. Alternatively,one or more other layers may be provided between the surface layer 104and the substrate layer 102. Optionally, the surface layer 104 mayinclude a coating either exterior of or interior of the graphene layer.The coating may be a metal compound coating such as gold, silver, tin,palladium, nickel, palladium-nickel, platinum and the like.

The surface layer 104 may include defects 110 that expose the substratelayer 102. The defects 110 are formed during the forming or depositingprocess. For example, the defects 110 may form at triple points, grainboundaries of the graphene layer 106, scratches in the graphene layer106, and the like. The size, shape and amount of defects 110 may dependon many factors, such as the grain size of the graphene, the method ofgrowing or forming the graphene, contamination and the like. The defects110 expose the substrate layer 102, which may lead to corrosion of thesubstrate layer 102 if left exposed. The boundary cappings 108 areselectively deposited only at the defects 110 as opposed to across theentire surface layer 104 to save cost of manufacture. The boundarycappings 108 inhibit corrosion in areas where the substrate layer 102would otherwise be exposed or susceptible to corrosion.

The defects 110 have a bottom 112, exposing the substrate layer 102, andsides 114 extending through the surface layer 104 from the bottom 112 toa top 116 of the surface layer 104 (the terms bottom and top arerelative to a particular orientation of the electrical conductor andmore generally constitute interior and exterior, respectively). Thesides 114 are exposed within the defects 110. While the defects 110 arerepresented graphically in FIG. 1 as being rectangular, it is realizedthat the defects 110 may have any shape, and typically will have acomplex shape. For example, the sides 114 may be non-planar and may beirregular in shape. The boundary cappings 108 are illustrated asentirely filling the defects 110, however the boundary cappings 108 mayonly partially fill the defects 110 and still cap the defect 110 toinhibit corrosion of the substrate layer 102. In an exemplaryembodiment, the boundary cappings 108 directly engage the substratelayer 102 at the bottom 112.

In an exemplary embodiment, the graphene layer 106 is the outermostlayer of the electrical conductor 100. The graphene layer 106 may reducefriction on the outermost surface of the electrical conductor 100, whichmay make mating of the electrical conductor 100 easier. The graphenelayer 106 may reduce stiction of the surface layer 104. The reduction instiction may allow use of the electrical conductor 100 in fields ordevices that previously were unsuitable for electrical conductors 100having problems with stiction and/or cold welds, such as electricalconductors having the outermost layer being a gold layer. For example,in microelectromechanical systems (MEMS) switches, stiction is a problemwhen a gold layer is the outermost layer of the electrical conductor.Coating the surface layer 104 with the graphene layer 106 reduces thestiction of the electrical conductor 100, making the electricalconductor suitable for use in MEMS switches.

FIG. 2 is a top view of a portion of the electrical conductor 100showing the graphene layer 106 and the boundary cappings 108 to inhibitcorrosion of the electrical conductor 100. FIG. 3 is an enlarged view ofa portion of the electrical conductor 100 shown in FIG. 2. The graphenelayer 106 is electrically conductive. The graphene layer 106 isdeposited on the substrate layer 102. In an exemplary embodiment, thegraphene layer 106 is grown on the substrate layer 102. For example, theelectrical conductor 100 is processed to grow the graphene layer 106 onthe entire surface of the substrate layer 102 or in select locations ofthe substrate layer 102.

In an exemplary embodiment, the graphene layer 106 may be formed duringa chemical vapor deposition (CVD) process in the presence of an organiccompound, such as gaseous methane, at a high temperature, such asapproximately 800° C. Deposition mechanisms may also include electronbeam, microwave or other process within the vaporous atmosphere. Otherprocesses may be used to deposit the graphene layer 106, such as laserdeposition, plasma deposition or other techniques or processes.Optionally, the graphene layer 106 may be 1 atomic layer thick on thesubstrate layer 102. Alternatively, the graphene layer 106 may bethicker. In an exemplary embodiment, the graphene layer 106 is depositeddirectly on the substrate layer 102 using the metal compound of thesubstrate layer 102 as a catalyst during the CVD process (or otherprocess) to promote graphene growth at the interface with the substratelayer 102. The type of organic compound or gas precursor used, thepressure of the gas precursor used, the flow rate of the gas precursor,the temperature of the process, or other factors may be selected topromote graphene growth on the particular metal type used for the metalsubstrate.

During the graphene growth, the defects 110 (shown in FIG. 1) naturallyoccur. For example, the defects 110 are defined at the grain boundaries130, scratches 132 of the graphene layer 106, pin-hole defects,contamination and the like. The defects 110 may have any size or shape.The scratch 132 almost entirely removes the graphene layer 106 in sucharea. The grain boundaries 130 have line structures and isolatedislands. In an exemplary embodiment, defect-free areas 120 are definedbetween the defects 110. The defect-free areas 120 are defined by thegraphene structure and provide blanket coverage of the substrate layer102 below the defect free areas 120. The defect-free areas 120 define amuch larger surface area of the surface layer 104 than the defects 110.The defects 110 tend to expose the underlying metal substrate of thesubstrate layer 102. If left uncapped, corrosion of the substrate layer102 may occur at the defects 110. Selective deposition of the boundarycappings 108 at the defects 110 inhibits corrosion at the defects 110.The surface layer 104 as a whole, including the graphene layer 106 andthe boundary cappings 108 provide better corrosion resistance than asurface layer without boundary cappings.

The boundary cappings 108 may be electrically conductive. For example,the boundary cappings 108 may be metal crystals, such as precious metalcrystals of nano-size or larger. The boundary cappings 108 may becarbon-based structures, such as graphene having smaller grain-size thanthe graphene layer 106 to allow for growth in the defects 110. In anexemplary embodiment, the boundary cappings 108 are deposited directlyon the substrate layer 102, such as the exposed portions of thesubstrate layer 102 within the defects 110. The boundary cappings 108inhibit corrosion of the exposed portion of the substrate layer 102 atthe defects 110. In an exemplary embodiment, the electrical conductor100 is processed to grow the boundary cappings 108 in select locations(e.g. on the exposed substrate layer 102 within the defects 110). Theboundary cappings 108 constitute deposits that are embedded in thegraphene layer 106. The boundary cappings 108 cap the defects 110, suchas by plugging the voids left by the defects 110. In an exemplaryembodiment, the boundary cappings 108 cover the bottoms 112 (shown inFIG. 1) of the defects 110.

In an exemplary embodiment, the boundary cappings 108 may be formedduring an electrodeposition process. The boundary cappings 108 may beformed from precious metal nanocrystals deposited directly on thesubstrate layer 102 at the defects 110. For example, the boundarycappings 108 may include gold, silver, platinum or other types ofprecious metals. The boundary cappings 108 may be deposited only on theexposed portions of the substrate layer 102 within the defects 110. Forexample, the materials at the defects 110 may be more chemically activethan the graphene at the defect-free areas 120. Nucleation of thematerial of the boundary cappings 108 occurs at the defects 110. Themetal compound of the substrate layer 102 may be used to promoteelectrodeposition of the metal nanocrystals during the process topromote boundary capping 108 deposition at the interface with thesubstrate layer 102 as compared to other layers, such as the graphenelayer 106. As such, the boundary cappings 108 may be selectivelydeposited on the electrical conductor 100 at the defects 110 as opposedto a blanket covering of the entire graphene layer 106, which reducesthe manufacture time, materials and cost. The boundary cappings 108provide corrosion resistance.

The boundary cappings 108 may be formed by other types of selectivedeposition processes in alternative embodiments. For example, theboundary cappings 108 may be formed by atomic layer deposition,selective absorption or self assembled monomer deposition where an oxideor other inert material is selectively deposited at the defects 110.Having an electrically insulating material just at the defects 110 wouldhave only a small effect on the bulk conductivity of the electricalconductor 100. The atomic layer deposition and self assembled monomerdeposition processes may use a precursor that selectively reacts withthe exposed portion of the substrate layer to deposit the boundarycappings 108 at the defects 110. In other alternative embodiments, theboundary cappings 108 may be deposited using a chemical reductionreaction or chemical vapor deposition (CVD) process, such as in thepresence of an organic compound, such as gaseous methane, at a hightemperature, such as approximately 800° C. Deposition mechanisms mayalso include electron beam, microwave or other process within thevaporous atmosphere. Other processes may be used to deposit the boundarycappings 108, such as laser deposition, plasma deposition or othertechniques or processes. Optionally, the boundary cappings 108 may be 1atomic layer thick in the defects 110.

FIG. 4 is a flow chart showing an exemplary method of manufacture of anelectrical conductor, such as the electrical conductor 100. The methodincludes providing 200 a substrate layer, such as the substrate layer102. The substrate layer may be a copper or copper alloy layer.

The method includes depositing 202 a graphene layer, such as thegraphene layer 106, on the substrate layer. The graphene layer may beformed by an electrodepositing process, a CVD process, a bonding processor another process. The graphene layer may completely cover thesubstrate layer or may selectively cover portions of the substratelayer. The graphene layer may be formed by growing or depositing one ormore graphene layers on the substrate layer. The substrate layer may actas a catalyst to promote growth of the graphene thereon.

The method includes selectively depositing 204 boundary cappings, suchas the boundary cappings 108, on defects of the graphene layer toinhibit corrosion of the substrate layer at the defects. The boundarycappings may be deposited on the substrate layer and/or the graphenelayer. The boundary cappings may be deposited by an electrodepositingprocess, a CVD process, a bonding process an atomic layer depositionprocess, a self assembled monomer deposition process or another process.The boundary cappings may be formed by growing or depositing one or moreboundary capping material in the graphene layer at the defects. Thesubstrate layer may act as a catalyst to promote growth or deposition ofthe boundary capping material at the exposed portions of the substratelayer exposed by the defects. The boundary capping material may beelectrically conductive or may be electrically insulative. In anexemplary embodiment, the boundary capping material is a precious metalmaterial and nano-size crystals of the precious metal are depositedduring the depositing process. The boundary capping material may begraphene or may be an oxide or an inert material. Once the defects arecapped by the boundary capping material, the substrate layer is nolonger exposed (or at least is less exposed) making the substrate layerless susceptible to corrosion.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. Dimensions, types of materials,orientations of the various components, and the number and positions ofthe various components described herein are intended to defineparameters of certain embodiments, and are by no means limiting and aremerely exemplary embodiments. Many other embodiments and modificationswithin the spirit and scope of the claims will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Moreover, in the following claims, theterms “first,” “second” and “third,” etc. are used merely as labels, andare not intended to impose numerical requirements on their objects.Further, the limitations of the following claims are not written inmeans—plus-function format and are not intended to be interpreted basedon 35 U.S.C. §112, sixth paragraph, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

What is claimed is:
 1. An electrical conductor comprising: a substratelayer; a graphene layer deposited on the substrate layer, the graphenelayer having defects exposing the substrate layer; and boundary cappingsat the defects, the boundary cappings inhibit corrosion of the substratelayer at the defects.
 2. The electrical conductor of claim 1, whereinthe boundary cappings comprise nano-sized crystals deposited only at thedefects.
 3. The electrical conductor of claim 1, wherein the boundarycappings are electrodeposited on exposed portions of the substrate layerat the defects.
 4. The electrical conductor of claim 1, wherein theexposed portions of the substrate layer at the defects act as a catalystto react with the boundary capping material to deposit the boundarycappings only at the defects.
 5. The electrical conductor of claim 1,wherein the boundary cappings are electrically conductive.
 6. Theelectrical conductor of claim 1, wherein the boundary cappings areelectrically insulative.
 7. The electrical conductor of claim 1, whereinthe boundary cappings are embedded within the graphene layer anddirectly engage the exposed portions of the substrate layer at a bottomof the defect.
 8. A method of manufacturing an electrical conductor, themethod comprising: providing a substrate layer; depositing a graphenelayer on the substrate layer; and selectively depositing boundarycappings on defects of the graphene layer to inhibit corrosion of thesubstrate layer at the defects.
 9. The method of claim 8, wherein theboundary cappings comprise nano-sized crystals deposited only at thedefects.
 10. The method of claim 8, wherein said selectively depositingboundary cappings comprises electrodepositing boundary cappings onexposed portions of the substrate layer at the defects.
 11. The methodof claim 8, wherein said selectively depositing boundary cappingscomprises reacting boundary capping material with exposed portions ofthe substrate layer at the defects to deposit the boundary cappings onlyat the defects.
 12. The method of claim 8, wherein said selectivelydepositing boundary cappings comprises selectively depositing boundarycappings of nano-sized crystals of precious metal using a process thatreacts the nano-sized crystals of precious metal with the substratelayer exposed at the defects and that does not react the nano-sizedcrystal of precious metal with the graphene layer.
 13. The method ofclaim 8, wherein said selectively depositing boundary cappings comprisesan atomic layer deposition process in select locations at the defects.14. The method of claim 8, wherein said selectively depositing boundarycappings comprises a self-assembled monomer process in select locationsat the defects.
 15. The method of claim 8, wherein said selectivelydepositing boundary cappings comprises providing a precursor that reactswith the substrate layer and the boundary capping material and that doesnot react with the graphene layer to selectively deposit the boundarycapping material at the locations of the defects where the substratelayer is exposed.
 16. The method of claim 8, wherein said selectivelydepositing boundary cappings comprises filling the defects with boundarycapping material such that the boundary capping material is depositeddirectly on the substrate layer in the graphene layer.
 17. The method ofclaim 8, wherein said depositing a graphene layer on the substrate layercomprises depositing of graphene layer with defect-free areas betweendefects of the graphene layer, said selectively depositing boundarycappings comprises selectively depositing boundary cappings on thedefects with the defect-free areas largely devoid of boundary cappings.18. A method of manufacturing an electrical conductor, the methodcomprising: providing a substrate layer; depositing a graphene layer onthe substrate layer, the graphene layer having defects exposing thesubstrate layer; and decorating the defects with metal boundary cappingsusing an electrodeposition process where crystals of the metal boundarycappings are deposited at the exposed portions of the substrate layer.19. The method of claim 18, wherein said decorating comprises reactingboundary capping material with exposed portions of the substrate layerat the defects to deposit the boundary cappings only at the defects. 20.The method of claim 18, wherein said decorating comprises selectivelydepositing boundary cappings of nano-sized crystals of precious metalusing the electrodeposition process to react the nano-sized crystals ofprecious metal with the substrate layer exposed at the defects.